i) Field of the Invention
The present invention relates to combustion technology of burners and the like that combust fuel gas.
ii) Description of the Related Art
Upon gas combustion, air has a high ratio to fuel gas in a lean mixture and a low ratio in a rich mixture. In combustion of lean mixtures, nitrogen oxides (NOx) in combustion exhaust gases can be less but the combustion is not stable. On the contrary, in combustion of rich mixtures, the combustion is stable. It is known in view of their characteristics to improve the stability of combustion together with to reduce NOx, and to hold flame in lean mixtures by flame in rich mixture.
Concerning such gas combustion, it is known that thick flame holes disposed at both sides of thin flame holes of a burner form retention flame and this retention flame retains the main flame on the thin flame holes side (for example, Japanese Unexamined Patent Application Publication No. 2010-261615).